The present invention relates to an apparatus, method and program for alarming decrease in tire air-pressure.
As a method for detecting decrease in tire air-pressure in a four-wheel vehicle such as a passenger car, it is known to directly install a pressure sensor on a wheel, for example. However, such method was not preferable since it costs much.
In Japanese Unexamined Patent Publication No. 305011/1988, it is disclosed a method for detecting decrease in tire air-pressure from wheel velocities of four-wheel tires mounted on a vehicle by utilizing a tire deflation warning system (DWS). The apparatus utilizes a principle that in the case a tire air-pressure is decreased, the dynamic loaded radius of a tire becomes smaller than that of a tire having normal internal pressure, thus the wheel velocity of the deflated tire is faster than that of other tires having normal pressures. However, the apparatus could not detect decrease in tire air-pressure in the case the air-pressures of all of four wheels with the apparatus are decreased.
Other than the above-described methods, it is known to combine the above-mentioned sensor with the apparatus for the purpose of detecting decrease in air-pressures as inexpensively and efficiently as possible. However, such method still costs much.